The present invention relates to an ignition timing control system for internal combustion engines, and more particularly to an ignition timing control system which senses knocking in an internal combustion engine and which controls an ignition timing of the internal combustion engine based on whether knocking is sensed.
A technique of controlling an ignition timing in a feedback manner is well known. This technique comprises the steps of sensing knocking in an internal combustion engine. The ignition timing is then retarded gradually from the basic ignition timing if the occurrence of knocking is determined in the internal combustion engine, or the ignition timing is adjusted to gradually approach an optimal ignition timing if no knocking is sensed. Thus, if knocking is occurring, the ignition timing is controlled to be retarded so as to prevent any greater knocking from occurring. In contrast, if no knocking is occurring, the ignition timing is advanced, thereby increasing an output of the internal combustion engine and decreasing the fuel consumption thereof.
This technique, however, is designed to control an ignition timing in accordance with a state of occurrence of knocking so as to be advanced or retarded by a predetermined amount of angle from the basic ignition timing determined based on a rotational speed of the internal combustion engine and a load thereon. Therefore, this technique has a disadvantage as described below.
That is, referring to FIG. 15, suppose that the engine load is suddenly changed from the state (A) to the state (B) when a driver has suddenly changed an operation amount of an accelerator, for example. Since the ignition timing is set based on a basic ignition timing (shown by a broken line in FIG. 15) and a retardation angle from the basic ignition timing gradually changes as described above, a retardation angle from the basic ignition timing hardly changes in such a short time. Therefore, the ignition timing has a value as shown by a point (P2) in FIG. 15. As a result, though the internal combustion engine has changed to an operating state where knocking is unlikely to occur, the ignition timing is set to an ignition timing point retarded by a predetermined amount from the basic ignition timing. This has caused a reduction in an output of and a loss of the torque of the internal combustion engine.